Electric arc furnace



a w M m mi Wm 8 W W /J y B J. JONAS ELECTRIC ARC FURNACE Filed Jan. 51.1951 June 6, 1933.

Patented June 6, 1933 PATENT orrics JULIUS JONAS, 01' will,

m: & 613,01 mm,

LAND

a lication Med January 31,1001, l i-1.1 Io.

-For operatin .a plurality of electric arc furnaces it has itherto beennecessary to use separate transformers for feedin the individualfurnaces, as it was regar ed as im possible to operate reliably inparallel several furnaces from a common transformer. For through theshort-circuiting of the transformer consequent on electrodes of onefurnace coming into contact with one another, the other furnaces willalso be without/voltage and, on the electrodes being separated till thecurrent is interrupted, the transformer, on account of the reduction inthe ampere turns,has such a considerable stray field that the current ofthe other furnaces is choked to a very considerable extent.

The present invention relates to a method of and means for 0 rating aplurality of flame arc furnaces ed in parallel from a common transformerover rectifiers, by which this disadvantage is overcome.

According to -the invention this is efiected by each flame arc furnacebein fed from a separate secondary windin an by the secondar windingsdispose on a common trans ormercore being extensively subdivided and thewinding parts being intimately intermixed, and furthermore b the two endterminals of each of the secon ary windings being connected to thecorresponding rectifier anodes over choking coils which are sointerlinked that the successive half waves of current of opposite phaseof the interlinked chokes magnetize their common iron core m theopposite sense, the flame arc furnaces associated with the secondarywindings-being connected up in a known manner between the centre pointof the secondarywindings and the rectifier cathode.

In the accompanyin drawing Fi 1 illustrates, in schematic fasion,'one'em iment of the invention wherein a plurality of electric arcfurnaces are supplied from separate rectifier elements fed from thecommon current supply transformer; and Fig. 2 illustrates, also inschematic fashion, another embodiment of the invention wherein theseparate rectifier elements of Fig. 1 are com: bined in a singlerectifier. 4

Referring now to the drawing by char- ABBIGIQB 1'0 AITIINGESELLSCHAFTBROWN 4 ,IL 10m STOCK QOHPANY Q1 SWITZER- inns-mic m rum uon 51am, m1111 Germany Iebruary 1, 1m.

actors of reference and considering first the mvention according to Fig.1, a and a, are flame arc furnaces workin in parallel, which are fedover the rectifiers 1, b, from the comformer limb opposite the rimarywinding. 7

Each of the secondary win ings d d feeds a rectifier b b the endterminals of the secondary windin s being connected over the interlinkedcho ing co1ls e e, to the associated rectifier anodes.- The centrepoints of the secondary windings are connected to the electrodes of theflame arc furnaces, the other electrodes being connected to the cathodesf f; of the rectifiers. A steadying choke g is preferably interposed inthe primar circuit of the feeding transformer.

T s interlinked. choking coils are so de signed that, in the case ofcontact, being established between the electrodes one fur nace, that isto say in the case of a short circuit, they can take up the full voltageof the secondary, winding, without the magnetming current assuming avalue which would endanger the operation of the-other furnace. Theintermixmg of the arts of the secondary windings is preferab y carriedso far that on the circuit of one furnace being interrupted, there willbe no ap reciable choking of the current of the secon furnace.

Instead of using a separate rectifier for each of the flame arc furnacesworking in parallel, a common rectifier having a suitable number ofanodes may of course be used. For example, as shown in Fig. 2 of thedrawing, the two rectifiers b 6, may be replaced by the single rectifierb having a single cathode f to which the lower electrodes of thefurnaces a a, are multiply connected. The elements, connections andoperation of Flg. 2 being otherwise as shown and described with respectto Fig. 1 of the drawing;Mi

Having now particularly descri and ascertained the nature of my ,saidinvention and in what manner the same is be performed, I declare thatwhat I C18.1lIl 1SZ- 1. In an electric furnace system, the com binationof an alternating current supply line, a transformer havin aplurality ofindependent mid-tapped windings each divided into a plurality ofsections and the respective sections of said windings being interlarded,a plurality of flame-arc electric furnaces each aving a pair ofco-operating electrodes, rectifying means,'means comprising one of saidwindings and said rectifying means for supplying direct current fromsa1d line to one 0 said furnaces, and means comprising another of saidwindin and said recti ing means for suppl ing irect current rom saidline to anot er of said furnaces.

2. Inan electric furnace system, the combination of an alternatingcurrent line, a plurality of electric flame-arc furnaces each aving apair of cooperating electrodes, electric current rectifying means, and atransformer comprising a piuralit of independent mid-tapped windings eacdivided into a plurality of sections on each side of the mid-tap thereofand the end terminals thereof being connected with the said rectifyingmeans to supply current thereto from" said line for conversion intodirect current and the supply thereof to the said pairs of electrodes toestablish and maintain an arc therebetween, one electrode of each of thesaid pairs being connected with the said rectifyin means and the otherelectrode thereof be ng connected with a different one of said mld-taps,and the respective sections of said windings being interlarded tothereby limit the rise of the inductance of any one thereof upon theoccurrence of an interruption of the are between the electrodes of thefurnace connected with another of said windings.

3. In an electric furnace system, the combination of an alternatingcurrent line, a plurality of electric flame-arc furnaces each aving apair of coo ratin electrodes, an

electric current recti r, an a transformer comprising a pluralit ofindependent mid-tapped windlngs eac divided :t-into a pluralit ofsections and the end terminals thereof ing connected with said rectifierto supply alternating current thereto from said line for conversion intodirect current and the supply thereof to the said pairs of electrodes toestablish and maintain an arc therebetween, one electrode of each ofsaid pairs being connected with the said rectifier and the otherelectrode thereof bein connected with a different one of said mi -taps,and the respective sections of said windings being interlarded tothereby limit the rise ofzgthe inductance of any one thereof upon theoccurrence-,of'an interru tion of the are between the electrodes of t efurnace connected with another of said windings.

4. In an electric furnace system, the combination of an alternatingcurrent line, a

plurality of flame-arc furnaces each having 'a pair of coo ratingelectrodes, an electric current recti or for each of saidfurnaoes, and atransformer comprisin a plurality of inde endent mid-tapped windingsequal in num r to and separately connected with the said rectifiers tosupply the latter with alternating current from said line for conversioninto direct current and the supply thereof to the said electrodes of theassociated ones of said furnaces to establish and maintain a flame-arcbetween such electrodes, each of said windings being divided into aplurality of sections on each side of the midtap thereof and thesections of the respective windings being interlarded to limit the riseof inductance of any one thereof upon the occurrence of an interru tionof the are between theelectrodes of a urnace connected with another ofsaid windings.

5. In an electric furnace system, the combination of an alternatingcurrent line, a plurality of electric flame-arc furnaces each having apair of cooperating electrodes, a rectifier for each of said furnaceshaving a cathode and a pair of anodes, a transformer comprising aprimary winding connected with said line and a plurality of independentmidtapped secondary windings corresponding in number to said rectifiersand having the end terminals thereof connected with the anodes thereofto supply alternating current from said line thereto for convensionthereby into direct current and the supply thereof to the electrodes ofthe corresponding ones of said rectifiers to cause the simultaneous flowof an arc between the said electrodes thereof, the said secondarywindings being divided into a plurality of sections on each side of.

the said mid-tap thereof and the respective sections of said windingsbeing interlarded to prevent such decrease of flow of currenttherethrough as would effect interruption of the are between theelectrodes of the furnace connected therewith upon the interruption ofthe arc between the electrodes of a furnace connected with another, anda reactance included in each of the said connections between the saidsecondary windin and the said anodes operative to limit t e flow ofcurrent therethrou h u n the occurrence of direct contact ":'of' t e eectrodos of the furnace connected therewith.

6. The combination with a plurality of flame-arc furnaces each having aplurality of cooperating electrodes, and an alternating current line, ofan electric current rectifier for each of said furnaces, a transformerhaving a lurality of'windings corresponding in num r to and separatelyconnected with the said rectifiers o rative to supply the latter withalternating current from said line for conversion into direct currentand the supply thereof to the said electrodes of the associated one ofsaid furnaces to establish and maintain a flame-arc between such IIIelectrodes, each of said windings being divided into a plurality ofsections and the sections of the respective windings being interlardedto limit the rise of the inductance of any one thereof upon occurrenceof an interruption of the are between the electrodes of a furnaceconnected with another of said windings, and reactor means included inthe connections between said rectifiers and the said windings tostabilize the said arcs.

7 The combination with a pair of flameare electric furnaces each havinga pair of cooperating electrodes, and an alternating current line, of anelectric current rectifier for each of said furnaces, each rectifiercomprising a cathode and a pair of anodes, a transformer having aprimary winding connected with said line and a pair of secondarywindings each havin a mid-tap and being divided into a plurality ofsections on each side of the mid-tap thereof, the sections of therespective windings being interlarded and the terminals thereof oppositeto the said mid-tap being separately connected with the anodes of one ofsaid rectifiers to supply the latter with alternating current from saidline for conversion into direct current and the supply thereof to thesaid electrodes of the associated one of said pair of furnaces toestablish and maintain a flame-arc between such electrodes, theeiectrodes of the said furnaces vbeing connected res ectively with thecathode and the mid-tap o the associated said rectitier and secondarywinding, and a pair of reactance coils arranged about a commonmagnetizable core included in said connections between each of the saidsecondary windings and the said anodes of the associated rectifier tothereby limit themagnetization of the core of said transformer upon theoccurrence of direct contact of the said cooperating electrodes, theconnection of the said coils of a pair with respect to each other beingsuch as to effect magnetization of the said common core in the oppositesense.

In testimony whereof I have hereunto subscribed my name this 20th day ofJanuary A. D. 1931.

JULIUS JONAS.

